This invention relates to an optical information recording medium which can record and read out information by a laser beam, a process for producing the same, a readout (or playback) apparatus for optical information recording media, and a process for reading out information from optical information recording media.
Recently, as means for writing and reading out information in compact discs, video discs, photosensitive members for laser beam printer, optical letter readout machines, etc., optical recording media applying a laser diode beam are practically used. In such optical recording media, a recording medium which absorbs a laser diode beam, that is, near infrared rays, is necessary. As the recording medium, there have been proposed recording media having an inorganic recording layer of tellurium, an alloy of tellurium, an alloy of bismuth, or the like, recording media having an organic dye-containing recording layer such as a phthalocyanine dye (U.S. Pat. No. 4,298,995), a naphthalocyanine dye (Japanese Patent Unexamined Publication No. Heisei 1-198391), etc.
But the optical recording media having an inorganic recording layer have problems in that improvement in productivity is difficult due to employing a process under vacuum such as vacuum deposition, sputtering, etc. for forming a thin film on a substrate, improvement in recording density is limited due to a large thermal conductivity of the recording layer, and tellurium, selenium, and the like are toxic substances requiring careful handling from the viewpoint of safety and health.
On the other hand, the recording media containing organic dyes (organic recording media) are inferior in properties such as durability and reflectance to the recording media having an inorganic recording layer (inorganic recording media). Further, the recording media containing organic dyes are insufficient in both durability and solubility of the dyes in a solvent. But such organic recording media seem to have possibility for overcoming the problems of the inorganic recording media. Thus, organic recording media having the same durability as the inorganic recording media and being able to be produced by spin coating or dip coating have been studied.
For example, there is proposed an optical recording medium having an organic thin film of various derivatives of naphthalocyanines having Al, Ga, In, Te, Si, Ge, Sn, Pb, etc. as a central metal (Japanese Patent Unexamined Publication No. Heisei 1-198391). But such a recording medium is impossible to read out 10.sup.5 times or more by a semiconductor laser beam at 1 mW of playback readout power.
Therefore, when organic recording media are used, there is produced a system wherein the playback readout power of 0.5 mW or less is used in order to reduce a damage for the organic recording medium layer. But when the playback laser beam of 0.5 mW or less is used, there arise various problems in that outer noises are easily introduced, no interchangeability exists for the apparatus using the playback readout power of 1 mW, and the like.
In order to improve readout light stability of the organic optical recording media, there is proposed an addition of a singlet oxygen quencher to a cyanine dye (Japanese Patent Examined Publication No. Heisei 1-21798). Such a method is effective for preventing the cyanine dye from deterioration by light but not effective for heat energy of laser beam of 1 mW.